The present invention relates to safety barriers, and in particular relates to safety fences and gates in which opened gates return automatically to a closed position. One particular use for hinges along this line is pedestrian traffic control in industrial work areas. For example, Federal regulatory authorities (e.g., OSHA and EPA) require extensive systems to control the path and flow of workers in industrial plants. Hinged gates and doors are often used to restrict movement in areas deemed dangerous or to seal off areas containing harmful materials. Typically these regulations are implemented by installing extensive railing systems painted in fluorescent colors, usually bright yellow.
A common feature of these systems are self-closing gates and doors. Currently, spring loaded gates which automatically close via the tension in the spring are most commonly used. Other types of gates that are known and could be used are gravity gates that close automatically via the action of gravity.
Gravity gates typically employ a cylindrical hinge consisting of at least two parts: a lower portion and an upper portion that rotates about an oblique junction upon the application of a rotational force. As the upper portion rotates, the two portions separate due to the oblique junction. The upper portion “rises” thereby storing potential energy which will cause the upper portion to “fall” or rotate back to a neutral position when the rotational force is terminated. Examples of such a gate are shown in U.S. Pat. No. 4,631,777 to Takimoto, U.S. Pat. No. 3,733,650 to Douglas and U.S. Pat. No. 4,991,259 to Finkelstein et al.
One problem associated with known gravity gates is common to all devices that employ moving parts: friction. In many instances the rotating portions of the hinges are in direct contact with one another which causes friction. If the portions are made of metal, as they often are, the friction could lead to premature failure of the hinge absent some form of external lubrication. External lubrication, most often in the form of grease, is messy and transitory thereby leading to frequent maintenance.
More recent designs of gravity gates incorporate polymers to reduce the weight of the hinge and friction. The Douglas, Takimoto and Finkelstein patents cited above discuss implementing polymers in the design of gravity gates. These patents discuss hinges that use polymer cams to translate rotational energy to potential energy. Although polymer cams reduce friction, polymer cams are far more susceptible to torsional failures than metallic cams. Furthermore, the devices of these patents utilize multiple polymeric parts which increases the likelihood of torsional failure. When these weaknesses are combined with the difficulties relating to machining and molding such intricate polymer parts, the impracticality of these hinges is readily apparent.
Another weakness of known hinge and gate designs is the free conduction of electricity. Many hinges and gates employ metal on metal contact which leads to the conduction of electricity. Such conduction can be fatal. For example, a hot wire falling on a metal railing could electrocute someone passing through a swing gate attached to the railing.